Content Addressed Storage device configured to maintain content address mapping

ABSTRACT

A content addressed storage device configured to maintain content address mapping is disclosed. A data object to be stored on the content addressed storage device and a local data object identifier by which the data object is known to the sending source are received from a sending source. A content address to be associated with the data object on the content addressed storage device is determined based at least in part on the contents of the data object. The data object is stored on the content addressed storage device in a storage location associated with the content address. A mapping that associates the local data object identifier with the content address is maintained on the content addressed storage device.

CROSS REFERENCE TO OTHER APPLICATIONS

This application is a continuation of co-pending U.S. patent applicationSer. No. 10/984,686, entitled CONTENT ADDRESSED STORAGE DEVICECONFIGURED TO MAINTAIN CONTENT ADDRESS MAPPING filed Nov. 8, 2004 whichis incorporated herein by reference for all purposes.

Co-pending U.S. patent application Ser. No. 10/984,687 entitled CONTENTADDRESSED STORAGE DEVICE WITH WEB SERVICES INTERFACE is incorporatedherein by reference for all purposes; and co-pending U.S. patentapplication Ser. No. 10/984,678 entitled IMPLEMENTING APPLICATIONSPECIFIC MANAGEMENT POLICIES ON A CONTENT ADDRESSED STORAGE DEVICE isincorporated herein by reference for all purposes.

FIELD OF THE INVENTION

The present invention relates generally to data storage. Morespecifically, a content addressable storage device configured tomaintain content address mapping disclosed.

BACKGROUND OF THE INVENTION

Content addressed storage (CAS) devices store typically fixed content ina storage server typically accessed via a network. An example is theCentera™ CAS device made and sold by EMC™ Corporation of Hopkinton,Mass. Typically, an application sends data to the CAS device to bestored, the CAS device determines a storage location by calculating a“content address” (CA) based at least in part on the content to bestored, after which the CAS device stores the content in the selectedlocation and returns the content address to the application that sentthe data. The content address is used like a claim check to enable thestoring application (or, in theory, another application to which the CAhas been provided) to retrieve (and in some cases perform other limitedoperations, e.g., delete) the previously stored content.

Under the typical approach described above, an application must beconfigured to receive the content address and track a mapping betweenthe content address and a local object identifier (e.g., a file nameand/or path) by which the stored data object is known on the localsystem on which the application is running. This limits the use of CASdevices to those applications configured to maintain such a mapping andconsumes time and resources on the local system. For some types ofapplication, the functionality for maintaining such a mapping mayalready exist or be relatively easy to incorporate, but for otherapplications the required level of data tracking may become an obstacleto using a CAS device for storage.

Therefore, there is a need for a way to enable applications to use a CASdevice for storage without requiring that the application maintain amapping between the content address associated with the data on the CASdevice and the local object identifier (e.g., local file system nameand/or path) of the data object on the local system on which theapplication is running.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the invention are disclosed in the followingdetailed description and the accompanying drawings.

FIG. 1 is a block diagram illustrating a typical prior art contentaddressed storage (CAS) device.

FIG. 2 is a block diagram of a content addressable storage deviceconfigured to maintain content address mapping.

FIG. 3 is a flow chart illustrating a process used in one embodiment tomaintain content mapping on a CAS device.

FIG. 4 is a flow chart illustrating a process used in one embodiment toprocess requests to access data stored on a CAS device.

FIG. 5 is a flow chart illustrating a process used in one embodiment tomap a local data object identifier to a corresponding content address.

FIG. 6 is a flow chart of a process used in one embodiment to store dataon a CAS device.

FIG. 7 is a flow chart of a process used in one embodiment to processrequests to access data on a CAS device that may be configured tomaintain a content map for some applications (or other sources) but notothers.

DETAILED DESCRIPTION

The invention can be implemented in numerous ways, including as aprocess, an apparatus, a system, a composition of matter, a computerreadable medium such as a computer readable storage medium or a computernetwork wherein program instructions are sent over optical or electroniccommunication links. In this specification, these implementations, orany other form that the invention may take, may be referred to astechniques. In general, the order of the steps of disclosed processesmay be altered within the scope of the invention.

A detailed description of one or more embodiments of the invention isprovided below along with accompanying figures that illustrate theprinciples of the invention. The invention is described in connectionwith such embodiments, but the invention is not limited to anyembodiment. The scope of the invention is limited only by the claims andthe invention encompasses numerous alternatives, modifications andequivalents. Numerous specific details are set forth in the followingdescription in order to provide a thorough understanding of theinvention. These details are provided for the purpose of example and theinvention may be practiced according to the claims without some or allof these specific details. For the purpose of clarity, technicalmaterial that is known in the technical fields related to the inventionhas not been described in detail so that the invention is notunnecessarily obscured.

A content addressable storage device configured to maintain contentaddress mapping disclosed. In one embodiment, a data object to be storedon the content addressed storage device and a local data objectidentifier by which the data object is known to the sending source(e.g., application) are received. A content address to be associatedwith the data object on the content addressed storage device isdetermined based at least in part on the contents of the data object.The data is stored object on the content addressed storage device in astorage location associated with the content address. A mapping thatassociates the local data object identifier with the content address ismaintained on the content addressed storage device.

FIG. 1 is a block diagram illustrating a typical prior art contentaddressed storage (CAS) device. An application 102 sends data to a CASdevice 104 to be stored. The CAS device 104 stores the data and returnsto the application 102 a content address (CA) associated with the data.The application 102 maintains a content map 106 that associates thelocal data object identifier (e.g., file name and/or path) associatedwith each file or other set of data sent to the CAS device 104 forstorage with the corresponding content address returned by the CASdevice 104 to the application 102 for the data. In the example shown, adata object “D:\data1” was stored by application 102 on CAS device 104and the content address “G45H433” was returned by CAS device 104 toindicate to application 102 where on the CAS device the data object“D:\data1” was stored. If in the future application 102 needed to accessthe data object “D:\data1” as stored on CAS device 104, application 102would look up the corresponding content address in the content map 106and use the content address to access the data on CAS device 104. Asnoted above, under the approach shown in FIG. 1, the application 102must be configured to maintain the content map 106, which requires thatadditional functionality be built into application 102 and consumesadditional memory and processing resources on the host(s) on whichapplication 102 is running.

FIG. 2 is a block diagram of a content addressable storage deviceconfigured to maintain content address mapping. An application 202 sendsdata to a CAS device 204 to be stored. The application provides inaddition a unique identifier associated with the application and a localdata object identifier by which the sent data is known to theapplication and/or a local host on which the application is running. TheCAS device 204 computes a content address based at least in part on thedata and stores the data in a location associated with the contentaddress. The CAS device 204 then stores in a content map 206 maintainedon the CAS device 204 for the sending application 202 an associationbetween the local data object identifier by which the application 202knows the data and the content address associated with the data on theCAS device 204. In the example shown, the content map 206 maintained onand by CAS device 204 for the application 202 is one of a plurality ofcontent maps 206-210 maintained by CAS device 204, one for eachapplication that has stored data on CAS device 204.

Each of the content maps 206-210 is identified by a unique applicationidentifier (e.g., “Application #345”) associated with the applicationwith which the content map is associated. Because the content map foreach application is maintained on and by the CAS device 204,applications such as application 202 need not be configured to maintaina mapping between content addresses generated by the content addressedstorage device and local data object identifiers. Instead, theapplication can simply access or refer to the data stored on the CAS bythe local data object identifier by which it is known on the local hoston which the application is running. This approach enables a contentaddressed storage device to be exposed on the local host as anadditional drive, for example, even though a CAS device typically doesnot have a native file system such as would otherwise be required toaccess the CAS device in the same way as a local drive. In the exampleshown in FIG. 2, once the data has been stored and the associatedcontent map updated, the CAS device 204 returns to the application 202an operation status report or message, e.g., one indicating the data was(or was not, if applicable) stored successfully.

In one embodiment, the application 202 accesses the CAS device 204 via anetwork, such as a TCP/IP network (not shown). The CAS device 204 has acommunication interface, such as a network interface card (NIC), tofacilitate such communication. The CAS device 204 in addition includes amemory used to store the content maps 206-210, one or more storage nodesconfigured to store data sent to the CAS device 204 by applications suchas application 202, and one or more processors configured to perform thedata storage, retrieval, and management functions of the CAS device 204and the content mapping operations described herein. One or more of theone or more processors may include a general purpose processor (e.g.,CPU) configured by software to perform such functions and operations,and/or an application specific integrated circuit, field programmablelogic device, or other device so configured.

FIG. 3 is a flow chart illustrating a process used in one embodiment tomaintain content mapping on a CAS device. In one embodiment, the processof FIG. 3 runs on a CAS device such as CAS device 204 of FIG. 2. Data isreceived (302). If the unique application identifier of the sendingapplication has been provided with the data and/or is otherwise known(e.g., based on other information received with the data, the connectionon which the data was received, etc.) (304), the data is stored (308).If the application identifier has not been provided and is not otherwiseknown (304), the application identifier is obtained (306) and the datais stored (308).

In one embodiment, each application generates its own identifier andprovides the identifier to the CAS device, which acknowledges andauthorizes the identifier if it is unique but instead rejects theidentifier and requests that the application propose a differentidentifier for the application in the event the identifier proposed bythe application is already associated on the CAS device with anotherapplication. In one alternative embodiment, the CAS device is configuredto generate a unique application identifier for each application withwhich it interacts. In one such embodiment, 306 includes generating aunique identifier for the application and informing the application ofthe unique identifier assigned to it, so that the application caninclude the unique identifier with future data sent to the CAS devicefor storage. In one embodiment, the application provides its uniqueidentifier by including the identifier in a prescribed header or otherfield of a message used by the application to send data to the CASdevice for storage. In one alternative embodiment, a third partyregistry or similar service assigns globally unique applicationidentifiers to registering applications. In one such embodiment, 306includes obtaining an identifier for the application from such a thirdparty and/or requesting that the application do so.

Storing the data (308) includes calculating a content address for thedata based at least in part on the content being stored. This contentaddress is associated on the CAS device with the local data objectidentifier (e.g., file name and/or path) by which the stored data objectis known to the sending application (e.g., the file name and/or path forthe data object on a local host on which the application is running)(310). The association between the content address and the correspondinglocal data object identifier is stored on the CAS device in a contentmap associated with the sending application (312). In one embodiment,310 and 312 are combined and the association between the content addressand the corresponding local data object identifier is made by storingthe corresponding values in associated locations in a content mapassociate with the sending application. A result of the operation isreported to the sending application (314), after which the next data tobe stored is received and processed (302). As noted above, the resultreported may include a report that the requested data storage operationwas completed successfully. There is no need to report the contentaddress, because the content map maintained on and by the CAS devicemakes it possible for the application to access (e.g., retrieve) datastored by the application on the CAS device by providing its applicationidentifier and the local data object identifier by which the data isknown to the application, as described more fully below.

FIG. 4 is a flow chart illustrating a process used in one embodiment toprocess requests to access data stored on a CAS device. A request toreceive a data object stored on the CAS device is received (402). In oneembodiment, the request includes an application identifier associatedwith the requesting application and a local data object identifier bywhich the requested data is known by the requesting application. Thelocal data object identifier is mapped to a corresponding contentaddress on the CAS device (404). The data is retrieved from a locationassociated with the content address (406) and provided to the requestingapplication (408).

FIG. 5 is a flow chart illustrating a process used in one embodiment tomap a local data object identifier to a corresponding content address.In one embodiment, the process of FIG. 5 is used to implement 404 ofFIG. 4. An application identifier associated with the requestingapplication is used to identify a content map associated with therequesting application (502). In one embodiment, the request includesand/or is accompanied by the application identifier of the requestingapplication. In one embodiment, the content map is maintained on and bythe CAS device. The content map is used to map a local data objectidentifier (e.g., file name and/or path) associated with the requesteddata to a corresponding content address on the CAS device (504). In oneembodiment, the local data object identifier is included in the requestreceived from the requesting application. The requesting applicationidentifies the data using the local data object identifier and thereforenever needs to learn or track the content address associated with thedata on the CAS device.

Referring to the example shown in FIG. 2, an application such asapplication 202 would access data in one embodiment by sending to theCAS device 204 a request identifying the data by the local data objectidentifier by which the data is known to the application 202 (e.g.,“D:\data1”) and providing the application identifier for the application(e.g., “345”). The CAS device 204 would then identify content map 206 asthe applicable content map, and then use content map 206 to map thelocal data object identifier included in the request to thecorresponding content address associated with the requested data on theCAS device 204 (e.g., by mapping object identifier “D:\data1” to contentaddress “G45H433”). The CAS device 204 would then use the contentaddress to retrieve the corresponding data and provide it to therequesting application 202 in response to the request.

FIG. 6 is a flow chart of a process used in one embodiment to store dataon a CAS device. In the example shown, an application (or otherrequesting process, system, or entity) may optionally be configured tomaintain a mapping of local data object identifiers to correspondingcontent addresses on the CAS device or instead to rely on the CAS deviceto maintain such a mapping for the application. This approach enablesthe CAS device to operate both with applications configured to maintainsuch a mapping, such as large data storage/backup applications and/orlegacy application configured to maintain such a mapping for data storeon a CAS device as well as with applications, such as lighter weightand/or newer applications, that are not configured to maintain such amapping. In one embodiment, the process of FIG. 6 is implemented on aCAS device such as CAS device 204 of FIG. 2. Data is received (602). Itis determined whether the application from which the data was receivedis one for which the CAS device is maintaining a content map (604). Inone embodiment, whether the data was received from a source (e.g.,application) for which the CAS device maintains a content map isdetermined by reading the value of a flag or other data field in aheader or other portion of a message used by the sending application tosend the data to the CAS device. In one embodiment, the determination ismade by determining whether the application supplied an applicationidentifier and concluding a content map is maintained on the CAS deviceif an application identifier is present. In one embodiment, thedetermination is made by using an application identifier associated withthe data to determine, e.g., by reading a table, whether the applicationis one for which a content map is maintained on the CAS device. The CASdevice may be configured to make such a determination either by anadministrator or user or, e.g., by the application itself, e.g., bysending one or more configuration messages as prescribed in aproprietary or publicly available API or other interface. If the datawas received from a source (e.g., application) for which a content mapis not maintained on the CAS device, the data is stored (606) and theassociated content address is reported to the sending application (608),after which the process is repeated for the next received data. If thedata was received from a source for which a content map is maintained onthe CAS device, the data is stored (610), the content address associatedwith the data on the CAS device is associated with the correspondinglocal data object identifier by which the data object is known to thesending application (or other source) (612), the content map maintainedon the CAS device for the sending application is updated (614), and theresult of the operation (e.g., success, failure, etc.) is reported tothe sending application (616), after which the process repeats for thenext received data.

FIG. 7 is a flow chart of a process used in one embodiment to processrequests to access data on a CAS device that may be configured tomaintain a content map for some applications (or other sources) but notothers. A request to access a data object stored on the CAS device isreceived (702). It is determined whether the requesting application (orother source) is one for which a content map is maintained on the CASdevice. In one embodiment, one or more of the approaches described abovein connection with 604 are used to make the determination in 704. In oneembodiment, the determination in 704 is made based on whether therequest includes a content address for the data object. If therequesting application is not one for which a content map is maintainedon the CAS device (704), the requested data is retrieved (e.g., using acontent address included in and/or provided with the request) andprovided to the requesting application (708), after which the processends. If the requesting application is one for which a content map ismaintained on the CAS device (704), the local data object identifierassociated with the request data is mapped to a corresponding contentaddress, e.g., using the content map maintained on the CAS device forthe requesting application (706), and the content address is used toretrieve the requested data and provide it to the requesting application(708), after which the process ends.

Using the approaches described herein, applications that are notconfigured to maintain a mapping of content addresses to local dataobject identifiers can still use a CAS device to store data, therebysimplifying application development, reducing consumption of resourceson the local host on which the application is running, and expanding theuniverse of applications able to use a CAS device for off-systemstorage.

Although the foregoing embodiments have been described in some detailfor purposes of clarity of understanding, the invention is not limitedto the details provided. There are many alternative ways of implementingthe invention. The disclosed embodiments are illustrative and notrestrictive.

1. A method for storing data on a content addressed storage device,comprising: receiving from a sending source a data object to be storedon the content addressed storage device and a local data objectidentifier by which the data object is known to the sending source;determining based at least in part on the contents of the data object acontent address to be associated with the data object on the contentaddressed storage device; storing the data object on the contentaddressed storage device in a storage location associated with thecontent address; and maintaining on the content addressed storage devicea mapping that associates the local data object identifier with thecontent address.
 2. A method as recited in claim 1, wherein the sendingsource comprises a sending application.
 3. A method as recited in claim1, wherein maintaining on the content addressed storage device a mappingthat associates the local data object identifier with the contentaddress comprises updating a content map associated with sending source.4. A method as recited in claim 1, wherein the local data objectidentifier includes a file name associated with the data object on alocal host associated with the sending source.
 5. A method as recited inclaim 1, wherein the local data object identifier includes a file pathassociated with the data object on a local host associated with thesending source.
 6. A method as recited in claim 1, wherein the dataobject comprises a file.
 7. A method as recited in claim 1, furthercomprising reporting to the sending source that the data object wasstored successfully.
 8. A method as recited in claim 1, furthercomprising determining whether a source identifier associated with thesending source is known and, if the source identifier is known, usingthe source identifier to identify a content map associated with thesending source, wherein said mapping is maintained in said content map.9. A method as recited in claim 1, further comprising: receiving from arequestor a request to access the data object, the request including thelocal data object identifier; using the mapping to determine the contentaddress associated with the local data object identifier; retrieving thedata object using the content address; and providing the data object tothe requestor.
 10. A method as recited in claim 9, wherein the requestoris the sending source.
 11. A method as recited in claim 10, wherein thesending source comprises a sending application.
 12. A content addressedstorage device, comprising: a communication interface configured toreceive from a sending source a data object to be stored on the contentaddressed storage device and a local data object identifier by which thedata object is known to the sending source; a memory; and a processorconfigured to: determine based at least in part on the contents of thedata object a content address to be associated with the data object onthe content addressed storage device; store the data object in thememory at a storage location associated with the content address; andmaintaining on the content addressed storage device a mapping thatassociates the local data object identifier with the content address.13. A content addressed storage device as recited in claim 12, whereinthe processor is configured to maintain on the content addressed storagedevice a mapping that associates the local data object identifier withthe content address at least in part by updating a content mapassociated with sending source.
 14. A content addressed storage deviceas recited in claim 12, wherein the processor is further configured toreport to the sending source that the data object was storedsuccessfully.
 15. A content addressed storage device as recited in claim12, wherein the processor is further configured to determine whether asource identifier associated with the sending source is known and, ifthe source identifier is known, use the source identifier to identify acontent map associated with the sending source, wherein said mapping ismaintained in said content map.
 16. A content addressed storage deviceas recited in claim 12, wherein: the communication interface is furtherconfigured to receive from a requester a request to access the dataobject, the request including the local data object identifier; and theprocessor is further configured to use the mapping to determine thecontent address associated with the local data object identifier,retrieve the data object using the content address, and provide the dataobject to the requester.
 17. A computer program product for storing dataon a content addressed storage device, the computer program productbeing embodied in a computer readable medium and comprising computerinstructions for: receiving from a sending source a data object to bestored on the content addressed storage device and a local data objectidentifier by which the data object is known to the sending source;determining based at least in part on the contents of the data object acontent address to be associated with the data object on the contentaddressed storage device; storing the data object on the contentaddressed storage device in a storage location associated with thecontent address; and maintaining on the content addressed storage devicea mapping that associates the local data object identifier with thecontent address.
 18. A computer program product as recited in claim 17,wherein maintaining on the content addressed storage device a mappingthat associates the local data object identifier with the contentaddress comprises updating a content map associated with sending source.19. A computer program product as recited in claim 17, furthercomprising computer instructions for reporting to the sending sourcethat the data object was stored successfully.
 20. A computer programproduct as recited in claim 17, further comprising computer instructionsfor determining whether a source identifier associated with the sendingsource is known and, if the source identifier is known, using the sourceidentifier to identify a content map associated with the sending source,wherein said mapping is maintained in said content map.
 21. A computerprogram product as recited in claim 17, further comprising computerinstructions for: receiving from a requestor a request to access thedata object, the request including the local data object identifier;using the mapping to determine the content address associated with thelocal data object identifier; retrieving the data object using thecontent address; and providing the data object to the requestor.